The invention relates to a planar Josephson device and a method of manufacturing thereof, which device comprises two layers of an oxidic superconducting material between which at least one non-superconducting layer is provided.
A method of manufacturing a Josephson device or Josephson junction is described in an article by M. G. Blamire et. al., in J. Phys. D: Appl. Phys. 20, pages 1330-1335 (1987). In this article, a sapphire substrate is provided with a buffer layer of Y.sub.2 O.sub.3 to which a first oxidic superconducting layer of YBa.sub.2 Cu.sub.3 O.sub.7-.delta. is applied. Subsequently, a thin layer of Y.sub.2 O.sub.3 is provided which serves as a tunnel barrier. Next, a second layer of YBa.sub.2 Cu.sub.3 O.sub.7-.delta. is applied, on which contacts of Nb may be provided. The thin layers are manufactured by means of dc magnetron sputtering using metallic target plates in an oxidizing atmosphere. Patterns are formed in the layers by means of plasma etching or ion etching.
In the oxidic superconducting materials known so far, the superconducting properties, in particular the highest temperature T.sub.C at which superconductivity occurs, are negatively influenced by the presence of a large number of metallic elements, silver and gold being two of the few exceptions. In particular a disturbance of the oxygen content seems to have undesirable effects. In the manufacture of devices such as a Josephson junction, in which a tunnel barrier is required, it must therefore be precluded that diffusion takes place from the tunnel barrier towards the superconducting material or that a reaction between the tunnel barrier and the superconducting material takes place. For this purpose buffer layers of a metal which passes oxygen such as silver can be used, however, this is not always sufficient at a high temperature.